Copper foil for printed-wiring board and copper-clad laminate using copper foil for printed-wiring board

ABSTRACT

The object is to provide a copper foil excellent in the property of selective etching between a resistor layer and a copper layer required in production of a printed-wiring board, and also excellent in UL heat resistance. For this purpose, a copper foil for printed-wiring board comprising a nodular treatment side on one side, wherein a nickel-zinc alloy layer is formed on the nodular treatment side is used for applications of printed-wiring boards. At the same time, a production method suitable for production of the copper foil is provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a national stage filing under 35 U.S.C. §371of PCT/JP02/07601, filed on Jul. 26, 2002, designating the U.S.

TECHNICAL FIELD

The present invention relates to a copper foil for printed-wiring boardand a method of producing the same, and a copper-clad laminate using thecopper foil for printed-wiring board.

BACKGROUND ART

For copper foils that have been conventionally used, a various kinds ofcopper foils are introduced to the market, and which copper foil shouldbe used has been determined depending on the uses of printed-wiringboards. They include, for example, copper foils comprising nickel layersfor forming resistors, heat-resisting copper foils to be used for sitesthat are exothermically affected in a direct manner by electronicequipment, and copper foils having excellent chemical resistance thatare advantageously used for formation of fine pitch circuits.

In the trend in recent years toward miniaturization of electricequipment, miniaturization is also required for the printed-wiring boardto be contained therein, and the formed copper foil circuit is furtherreduced in width. Furthermore, as computers operate faster, theprocessing speed is also enhanced, and clock frequencies arecontinuously increasing. Thus, for keeping up with improvement inperformance of computer apparatuses, and achieving furtherminiaturization, provision of fine pitch circuits having increasedwiring densities becomes essential.

As the wiring density of the printed-wiring board is increased andcomponents implemented therein are further integrated, the amount ofheat generation is increased, thus causing a problem. For example, thestrength of bonding between the copper foil forming the circuit of theprinted-wiring board and a substrate is reduced with time, and in someextreme cases, the copper foil circuit may be peeled off spontaneouslyfrom the base material. Therefore, current materials for printed-wiringboards are subjected to a variety of treatments to prevent problemsbefore they happen.

The printed-wiring board can be considered as a composite productcomposed of a metal and a resin material, and thus improvement of itsheat resistance will be influenced by a variety of factors such as thecomposition of the resin material and the type of surface treatment ofthe cupper foil. As copper foils having excellent heat resistance forprinted-wiring boards, those having thick zinc layers or brass layersformed on nodular treatment sides thereof have been widely known. Thatis, the heat resistance with respect to the printed-wiring boardgenerally refers to that of the product conforming to UL Standard. Thethick zinc layer or brass layer provided on the nodular treatment sideof the copper foil for ensuring conformation to UL Standard exhibitsexcellent performance to secure heat resistance.

On the other hand, in formation of small fine pitch circuits, theprinted-wiring board comprising a 50-μm pitch signal transmissioncircuit with its circuit width of 25 μm and its inter-circuit gap of 25μm has also commonly produced. Thin copper foils have been used inproduction of printed-wiring boards comprising such fine circuitsbecause a satisfactory etching property is required when the copper foilis etched to form a circuit. Also, the additive method has been widelyused in which an outer-layer copper foil is once completely etched away,and thereafter the copper foil circuit is formed by the plating methodor the like.

However, for processing fine via holes and the like, laser drillingprocessing has been used in recent years, thus making it difficult toprocess the via hole with the copper foil bonded thereto, and thereforethe conformal mask method in which the outer-layer copper foil ispartially etched away to carry out laser drilling processing, the methodin which the outer-layer copper foil for improving accuracy of positionfor drilling process is wholly etched away, and so on are employed.Then, after laser drilling processing is carried out, a copper layer isformed through the panel plating method and patterned to form a circuitin the site in which the copper foil has been etched away, or a copperfoil circuit is directly formed by the additive method.

The problem arising in such methods is that after the copper foil isonce removed, a surface treatment layer that would exist if the originalcopper foil were used does not exist in the interface between thecircuit formed by the panel plating method or the additive method andthe substrate. That is, absence of the surface treatment layer meansthat in the circuit portion is provided no means for purposely improvingits chemical resistance and heat resistance.

Therefore, in particular, the heat resistance property of that circuitportion is significantly reduced compared to the case where a normalcopper foil having improved heat resistance is used, and materials andmethods preventing such a problem from arising have been desired.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 8 are schematic sectional views of copper foils forprinted-wiring boards according to the present invention.

FIGS. 2 to 7 are each presented as a flow chart showing a process forproducing a printed-wiring board that is used in the followingdescription.

SUMMARY OF THE INVENTION

Then, as a result of conducting vigorous studies, the inventors of thepresent invention have considered that the above described problem canbe solved by providing a copper foil comprising a nickel-zinc alloylayer on the nodular treatment side. The present invention will bedescribed below.

In claims is described a copper foil for printed-wiring board comprisingon one side a nodular treatment side to be bonded to a substrate,characterized in that a nickel-zinc alloy layer is provided on thenodular treatment side. FIG. 1 is a schematic sectional view showingthis copper foil for printed-wiring board.

Here, the description of “a nickel-zinc alloy layer is provided on thenodular treatment side” implies that nodular treatment is applied to oneside of a copper foil 2, and then a nickel-zinc alloy layer 5 is formedon the surface obtained after the nodular treatment. The term “nodulartreatment” used herein means a treatment for providing irregularitiesformed on the bonding side of the copper foil when the copper foil andthe substrate are bonded together for producing a copper clad laminate.Formation of the irregularities is generally carried out by depositingcopper microparticles 4 on the surface by electrolysis. The method canalso be employed in which the one side of the copper foil layer 2 isetched, thereby providing only one side of the copper foil layer 2 witha matte face.

Then, the “nickel-zinc alloy layer” is formed on the side subjected tonodular treatment, whereby the selective etching property is ensured,and the heat resistance specified in UL 796 Standard (hereinafterreferred to as “UL heat resistance” is ensured at the same time. Theterm “selective etching property” described in this specification isused to imply that only the copper component is dissolved, and nickel ora nickel-zinc alloy is not dissolved.

This selective etching property functions as a very useful property inthe method of printed-wiring boards described later.

Up to this time, the concept of using nickel or a nickel-zinc alloy forsurface treatment of the copper foil has been adopted for improvingchemical resistance mainly in the sense that no damage is caused bychemical solutions used in the process of production of theprinted-wiring board. As a result of conducting vigorous studies, theinventors of this invention have envisioned a certain method ofproducing printer-wiring plates, and considered that in the method, aprotective layer for ensuring heat resistance could be left below theformed circuit even if the panel plating method or additive method isused. Thus, explanation will be presented showing the method of usingthis copper foil for printed-wiring board.

FIG. 2A shows a so called four-layer plate 11 in which a copper foil forprinted-wiring board 1 according to this invention is bonded to the bothouter faces of a core substrate 8 comprising an inner circuit 7, andshows therebelow a flow for subjecting this substrate to laser drillingprocessing to form a via hole 14 so as to produce a printed-wiring board18 having a fine pitch pattern.

For the four-layer plate 11 shown in FIG. 2A, copper foil layers 2 onthe both outer faces and the copper component of copper microparticles 4are first etched away for carrying out laser drilling processing. At thetime of etching them away, if an acid etchant such as a ferric chloridesolution and copper sulfate based solution being a normal etchant foretching copper, the nickel-zinc alloy layer 5 as a surface treatmentlayer is also dissolved away along with the copper component, leading toa result similar to that when a conventional normal copper foil is used.However, if so called an alkali etchant or sulfuric acid-hydrogenperoxide based solution is used as an etchant for etching copper, thenickel or nickel-zinc alloy layer 5 remains without being dissolved, andthe nickel or nickel-zinc alloy 5 appears on the both outer faces asshown in FIG. 3B.

The surface treatment applied to the matte side 3 of the copper foillayer 2 has never unnecessarily increased the amount of corrosionpreventing elements except for the case where surface treatment iscarried out using zinc or a zinc alloy for ensuring heat resistance.Therefore, the amount of deposited nickel or nickel alloy layer 5 issmall, and the nickel or nickel alloy layer 5 is not found to remain onthe surface of the substrate, and it can be said that all the layer isremoved including the surface treatment layer. In the case of thepresent invention, however, the nickel or nickel alloy layer 5 should bemade to remain in a recognizable way.

Then, in the case of the copper foil for printed-wiring board 1, itscomposition is also important. A nickel-zinc alloy has 70 to 88 wt % ofnickel and the balance of zinc is preferably used for the nickel-zincalloy. If the content of nickel in the nickel-zinc alloy is smaller than70 wt %, the content of zinc increases, and it becomes impossible tocarry out selective etching described above although UL heat resistanceis more advantageously ensured. On the other hand, if the content ofnickel in the nickel-zinc alloy exceeds 88 wt %, then the content ofzinc decreases. In this case, even though the selective etching propertyis quite excellent, the UL heat resistance does not satisfy the valuespecified in the Standard.

Also, the thickness of the nickel-zinc alloy is very important. Thecopper foil for printed-wiring board is characterized in that thethickness of the nickel-zinc alloy is 0.07 g to 45 g per square meter ofnodular treatment side of the copper foil. The thickness should benormally expressed using units for length such as μm, but the nodulartreatment side of the copper foil has irregularities as apparent fromFIG. 1, and copper microparticles are deposited thereon for obtaining ananchor effect when it is bonded to the substrate, thus making itdifficult to use a unit for length. Thus, the deposited amount persquare meter is used as a unit corresponding to the thickness of thenickel-zinc alloy layer.

The specific surface area of the nodular treatment side of a generalcopper foil varies depending on the thickness of the copper foil.Therefore, if the thickness of the nickel-zinc alloy layer is smallerthan 0.7 g per square meter of nodular treatment side of the copperfoil, stability is reduced in the sense that the nodular treatment sideof the normally conceivable whole thickness of copper foil is covereduniformly and without irregularity. If the thickness of the nickel-zincalloy layer exceeds 45 g per square meter, the irregularities forobtaining the anchor effect of the nodular treatment side of thenormally conceivable whole thickness of copper foil may be eliminated orchanged into a flat shape. Thus, the thickness derived as optimumconditions allowing the nickel-zinc alloy layer to be formed as asurface treatment layer for the nodular treatment side of the normallyconceivable whole thickness of copper foil is 0.7 g to 45 g per squaremeter of nodular treatment side of the copper foil.

Then, a laser beam is applied to a predetermined location to carry outlaser drilling processing. It is known that drilling processing with theuse of a carbon dioxide gas is difficult if the copper foil exists. Onthe other hand, the inventors of this invention have recommended nickelas a material enabling drilling processing to be carried out quiteeasily. A theory demonstrating that the nickel layer or nickel alloylayer has excellent laser drilling processability has not yet beenestablished. In the process of continuous studies, however, theinventors of this invention have come to believe that the laser drillingprocessability is improved based on the following principle.

When a metal is subjected to drilling processing by a laser, a processin which the metal is continuously vaporized in an amount correspondingto predetermined thickness of metal layer must be reproduced. In otherwords, during application of a laser, the temperature of at least thesite to which the laser is applied must be higher than the boiling pointof nickel or the nickel alloy. Copper that can hardly be subjected tolaser drilling processing is an element classified as a precious metalbelonging to the IB group of the periodic law, and has as its propertiesa melting point of 1083° C., a boiling point of 2582° C., and a meltingenthalpy (heat of melting) of 13.3 kJ/mol under the condition of1.01×10⁵ Pa.

On the other hand, nickel is classified as an element belonging to theVIII group of the periodic law, and has as its properties a meltingpoint of 1455° C., a boiling point of 2731° C., and a melting enthalpy(heat of melting) of 17.6 kJ/mol under the condition of 1.01×10⁵ Pa. Theboiling point of nickel is about 150 to 160° C. higher than the boilingpoint of copper. So far as these properties are concerned, nickel andthe nickel alloy are more stable than copper with respect to heat.Therefore, drilling processing using a laser beam is carried out byproviding high energy to the site exposed to the laser beam, therebysharply increasing the temperature of the site to cause the material ofthe site to be melted and vaporized, and therefore it cannot be thoughtthat the assumption that nickel and the nickel alloy are more easilydrilled than copper holds.

Here, the thermal conductivity of copper is compared to that of nickel.Copper has thermal conductivity of 354 W·m⁻¹·K⁻¹ at 700° C., and is agood heat conductor. On the other hand, nickel has thermal conductivityof 71 W·m⁻¹·K⁻¹ at 700° C., which is approximately ⅕ of the thermalconductivity of copper, and it can be understood that nickel has verylow heat conductivity compared to copper. In view of this fact, it canbe considered that copper being a good heat conductor quickly diffusesheat given by the laser beam, thus making it difficult for concentratedheat to remain in one site. Then, it is also known that nickel has highabsorptance for laser beams compared to copper. From these facts, it canbe considered that because copper has low absorptance for laser beams,and heat energy supplied to the copper foil site exposed to the laserbeam decreases causing heat given to the copper foil layer to be defusedquickly, the temperature of the site in the copper foil exposed to laserbeam hardly rises above the boiling point to reduce laser drillingprocessability.

Nickel conducts heat at a rate about ⅕ of the heat conductivity ofcopper. Also, because of its high absorptance for laser beams, nickelhas a high efficiency of conversion to heat energy compared to copper.Therefore, it can be considered that heat energy is easily concentratedon the site exposed to the laser beam, and the speed at which heatenergy is supplied by the laser beam than the speed at which heat isdiffused, and the site exposed to the laser beam easily reaches themelting point of nickel, thus improving laser drilling processability.If the aforementioned absorptance for laser beams is compared for copperand nickel having same levels of surface roughness, the reflectivity ofnickel is apparently smaller than that of copper by about 1% to 2%, andthus the absorptance for laser beams by nickel is higher.

As a result, it can be considered that nickel undergoes quicktemperature rising by application of a laser beam, and is easily meltedand vaporized in spite of the fact that its melting point is higher thanthat of copper. Therefore, a similar result can be obtained if anickel-zinc alloy having the composition mentioned in the presentinvention, existence of the alloy layer on the outer face of thesubstrate does not hinder at all laser drilling processability. FIG. 3Cshows a situation in which laser drilling processing is carried out toform the via hole 14, and desmear treatment is carried out.

Here, what is brought about as another effect is that a solution capableof dissolving the resin of the insulation resin layer is used for thesolution of desmear treatment, and therefore it vanishes evenirregularities on the outer face of the substrate, thus reducing theadhesion to the substrate of a copper layer subsequently formed by theplating method or the like. If using copper foil for printed-wiringboard according to present invention, however, irregularities on theouter face of the substrate remain intact so that the anchor effect canbe obtained because the nickel-zinc alloy layer exists on the outermostlayer, thus making it possible to improve adhesion between the platedlayer and the substrate.

From this point, a copper plated layer is formed on the entire surfaceof the substrate including the inner wall of the via hole 14 in the caseof the plating method, as shown in FIG. 4D. Then, as shown in FIG. 4E,an etching resist layer 16 is formed on the surface of the copper platedlayer 15, and as shown in FIG. 5F, a circuit pattern is developed bylight exposure on the etching resist layer 16, and a acid etchant forcopper is used to carry out circuit etching, and the etching resist ispeeled off to obtain the printed-wiring board 18 as shown in FIG. 15G.If the above described production method is adopted, the nickel-zinclayer 5 exists in the interface between the circuit on the outer faceand the substrate, thus making it possible to obtain a plate havingexcellent UL heat resistance.

When the semiadditive method is adopted, on the other hand, thefollowing flow is applied. For the plate shown in FIG. 3C that has beensubjected to laser drilling processing to form the shape of the via hole14 and has undergone desmear treatment, the etching resist layer 16 isformed on the surface of the exposed nickel-zinc layer 5 as shown inFIG. 6D without forming a plated layer, a circuit pattern is developedby light exposure on the etching resist layer 16 as shown in FIG. 6E,the nickel-zinc layer 5 is etched into a circuit shape using an etchant,and the etching resist is peeled off to provide a situation shown inFIG. 7F. Then, the copper plated layer 15 is formed on the nickel-zinclayer 5 shaped like a circuit and on the inner wall of the via hole 14,whereby the printed-wiring board 18 as shown in FIG. 7G can be obtained.Adoption of this production method makes it possible to obtain a platehaving excellent UL heat resistance in which the nickel-zinc layer 5exists in the interface between the circuit and the substrate in a sameway as FIG. 5G.

If assuming the uses described above, a copper foil in which a surfacetreatment layer capable of undergoing selective etching with copper isprovided, and the UL heat resistance of the surface treatment layer isexcellent is required. Therefore, a copper foil having those propertiestogether is the copper foil for printed-wiring board defined in claims.Furthermore, all the copper foils can be formed into copper cladlaminates, and processed into printed-wiring boards by normal etchingprocess, and in this case, excellent UL heat resistance is also ensured.

In addition, a copper foil having a similar effect is the copper foilfor printed-wiring board comprising on one side a nodular treatment sideto be bonded to a substrate according to another claim, characterized inthat a nickel layer is provided on the nodular treatment side, and azinc layer or a zinc alloy layer is provided on the nickel layer. FIG. 8shows a schematic sectional view of this copper foil. As apparent fromFIG. 8, the nickel layer 5 is provided on the nodular treatment side,and a zinc layer or a zinc alloy layer 19 typically of brass or the likeis provided on the nickel layer 5 as a surface treatment layer. Thenickel layer 5 serves to protect the zinc layer or zinc alloy layer 19typically of brass provided for the purpose of ensuring UL heatresistance when the copper component of the copper foil is subjected toselective etching with respect to the four-layer plate 11 shown in FIG.2A.

Therefore, uses similar to those of the copper foils described above canbe adopted for this copper foil for printed-wiring board, and theprinted-wiring board obtained by a production method similar to thosedescribed above allows a fine pitch circuit to be easily formed, andenables a circuit having UL heat resistance to be provided.

For this copper foil for printed-wiring board, however, the nickel layerand the surface treatment layer dependently of each other, and thereforeunless the total thickness of the nickel layer and surface treatmentlayer formed on the nodular treatment side of the copper foil isconsidered, irregularities on the nodular treatment side are vanished,and the anchor effect of the plated layer can no longer be obtained whenthe copper foil is processed into the printed-wiring board. Thus, thepresent invention provides a copper foil for printed-wiring board inwhich the weight thickness (X) of the nickel layer is in the range offrom 0.7 g/m² to 45 g/m², the weight thickness (Y) of the zinc layer isin the range of from 0.01 g/m² to 2 g/m², and the reduced thickness (T)calculated from Equation 1 is smaller than or equal to 5 μm, andprovides a copper foil for printed-wiring board in which the weightthickness (X) of the nickel layer is in the range of from 0.7 g/m² to 45g/m², the weight thickness (Z) of the zinc alloy layer containing nkinds of alloying elements is in the range of from 0.01 g/m2 to 2 g/m2,and the reduced thickness (T) calculated in accordance with theprocedure shown in Equation 2 is smaller than or equal to 5 μm, therebyspecifying their appropriate thickness. The nickel layer has a minimumthickness of 0.7 g/m² for achieving a uniform and defect-free thicknessin consideration of the selective etching property. At this time, theminimum necessary thickness of the zinc layer or zinc alloy layerrequired for conforming to the Standard of UL heat resistance is 0.01g/m². Thus, the reason why the expression has been used such that thetotal thickness is “smaller than or equal to 5 μm” is that the lowerlimit of total thickness is spontaneously determined from the minimumnecessary value in the range of weight thickness of nickel, zinc or thezinc alloy.

Unless the total thickness of the nickel layer and the zinc layer or thezinc alloy layer is considered, irregularities on the nodular treatmentside of the copper foil are vanished, and adhesion of the copper foilcan no longer be ensured when the copper foil is processed into thecopper clad laminate. As described previously, because irregularitiesare provided on the nodular treatment side of the copper foil, it isdifficult to express the thickness using gage thickness of the nickellayer and the zinc layer, and thus weight thickness is usually used.Thus, the total thickness of the nickel layer and the zinc layer or thezinc alloy layer is considered using this weight thickness.

However, the concept of total thickness is different for the case ofcombination of the nickel layer and zinc layer in the nodular treatmentside of the copper foil and the case of combination of the nickel layerand zinc alloy layer in the nodular treatment side of the copper foil.

First, the thickness in the case of combination of the nickel layer andzinc layer in the nodular treatment side of the copper foil isconsidered in the following manner. In reality, however, it is difficultto calculate correct thickness in a plane surface having smallirregularities, and therefore the thickness is reduced into a value thatwould be determined for a flat surface with experimental empiricalvalues taken into consideration. Here, the Ni layer is formed inthickness of X (g) per square meter, and its reduced thickness equalsX/8.85 (μm) provided that the specific gravity of nickel is 8.85 g/m³.If the Zn layer is formed on the nickel layer in thickness of Y (g) persquare meter, then its thickness equals Y/7.12 (μm). Therefore, thetotal thickness of the Ni layer and zinc layer equals (X/8.85)+(Y/7.12)(μm).

Next, the thickness in the case of combination of the nickel layer andzinc alloy layer in the nodular treatment side of the copper foil isconsidered in the following manner. Here, the zinc alloy is consideredas an alloy of Zn and n kinds of different metals. It is considered thatthe zinc alloy is deposited in thickness of Z (g) per square meter.Then, assume that the content of zinc in the zinc alloy is a % byweight, and the contents of constituent elements of n kinds of differentmetals (Me₁, Me₂, . . . , Me_(n)) are b₁% by weight, b₂% by weight, . .. , b_(n)% by weight, respectively. That is, the equation of a +(b₁+b₂+. . . +b_(n))=100 wt % holds. Then, the specific gravity ρ_(sum) of thealloy is given by equation 3. $\begin{matrix}{\rho_{sum} = {\frac{\left\{ {{7.12 \times a} + \left( {{\rho_{Me1} \times b_{1}} + {\rho_{Me2} \times b_{2}} + \ldots + {\rho_{Men} \times b_{n}}} \right)} \right\}}{100}.}} & {{Equation}\quad 3}\end{matrix}$

Therefore, the reduced thickness of the zinc alloy layer is consideredas X/ρ_(sum) (μm). From these considerations, the total thickness of thenickel layer and the zinc alloy layer is calculated as(X/8.85)+(Z/ρ_(sum)) (μm).

Experience shows if the reduced total thickness described above islarger than 5μ, irregularities on the nodular treatment side of thecopper foil are vanished. On the other hand, even if the thickness ofthe nickel layer is larger than 45 g/m², it contributes neither toimprovement of the selective etching property nor to stability ofthickness. In addition, nickel is expensive, and therefore it is desiredthat the amount of nickel to be used is reduced wherever possible. Forthese reasons, the upper limit of weight thickness (X) of the nickellayer is 45 g/m². When the upper limit of thickness of the nickel layeris determined, the upper limit of thickness of the zinc layer or zincalloy layer required for satisfying the conditions of total thicknessdescribed above is inevitably determined.

The copper foil for printed-wiring board described above exhibits itsproperties advantageously particularly in the uses as described above,but is also capable of adapting to other uses similar to those of usualcopper foils, and the printed-wiring board obtained from the copper cladlaminate produced using the copper foil for printed-wiring board hasexcellent UL heat resistance. Thus, one aspect of the present inventionprovides a copper clad laminate using the copper foil for printed-wiringboard wherein the copper clad laminate includes the concepts of bothrigid type and flexible type, and covers any layer structures ofsingle-sided, double-sided and multilayered structures.

BEST MODE FOR CARRYING OUT THE INVENTION

The results of producing a copper foil for printed-wiring boardaccording to the present invention, producing a multilayerprinted-wiring board, and measuring UL heat resistance will be describedbelow.

EXAMPLE 1

In this Example, the steps of producing a printed-wiring board using acopper foil for printed-wiring board comprising an alloy layer of nickeland zinc on the matte side of an electrodeposited copper foil will bedescribed. First, production of the copper foil for printed-wiring board1 will be described with reference to the drawings. Here, anelectrodeposited copper foil having a cross section shown schematicallyin FIG. 1 for use in producing a copper foil having nominal thickness of18 μm, which had not been subjected to surface treatment (hereinafterreferred to as “untreated copper foil”) was used. Then, a so calledsurface treatment apparatus was used to subject this untreated copperfoil 2 to nodular treatment and surface treatment for forming thenickel-zinc layer.

In the surface treatment apparatus, copper microparticles 4 are firstdeposited on the surface of the matte side 3 of the untreated copperfoil 2 under burnt copper plating conditions. For the burnt copperplating conditions for the copper microparticles 4, plating was carriedout under conditions of current density of 30 A/dm² and electrolysistime of 4 seconds by using an insoluble anode (DSE) for the counterelectrode to make the copper foil itself undergo cathode polarization,in a copper sulfate solution at a liquid temperature of 30° C. withconcentrations of copper and sulfuric acid being 12 g/l and 180 g/l,respectively.

Then, the nickel-zinc alloy layer 5 was formed on the surface with thecopper microparticles 4 provided thereon. For this nickel-zinc alloylayer 5, a pyrophosphate based solution was prepared with the use ofzinc pyrophosphate (ZnP₂O₇·3H₂O), nickel sulfate (NiSO₄·7H₂O) andpotassium pyrophosphate (K₂P₄O₇) so that the solution had a compositionwith 1.0 g/l of zinc, 10.0 g/l of nickel and 100 g/l of potassiumpyrophosphate, and in the solution at a liquid temperature of 30° C.,the copper foil itself was made to undergo cathode polarization with theuse of a stainless plate for the counter electrode under conditions ofcurrent density of 1 A/dm² and electrolysis time of 300 seconds, therebyproviding an alloy composition with 2.28 g/m² (70.1 wt %) of nickel and0.95 g/cm² (29.9 wt %) of zinc. The weight thickness of the nickel-zincalloy layer 5 was 3.23 g/m². In concurrence with this formation of thenickel-zinc alloy layer 5 on the nodular treatment side 4, 0.10 g/m² ofnickel-zinc layer was formed on the shiny side 6 of the untreated copperfoil 2 as a corrosion prevention layer. In addition, the surface withthe nickel-zinc alloy layer 5 formed thereon was treated with a silanecoupling agent and then dried to produce the copper foil forprinted-wiring board 1 shown in FIG. 1. However, the nickel-zinc alloylayer 5 formed on the surface of the shiny side 6, and the silanecoupling agent treated layer are not shown in the drawings.

The steps of producing a printed-wiring board using the copper foil forprinted-wiring board obtained in the above described steps will bedescribed below referring to FIGS. 2 to 5. The copper foil forprinted-wiring board 1 according to the present invention was bonded tothe both outer faces of a core substrate 8 comprising an inner circuit 7with an insulation layer 10 formed wit the use of a prepreg 9 underusual hot press conditions, and thereby a so called four-layer plate 11shown in FIG. 2A was produced.

Then, for the four-layer plate 11 shown in FIG. 2A, the copper componentof the untreated copper foil 2 and the copper microparticles 4 on theboth outer faces were first etched away for carrying out laser drillingprocessing. At the time when the copper component was etched away, “A”process solution (manufactured by Meltex Co., Ltd.) being so called analkali etchant was used as a etchant for copper, thereby allowing thenickel-zinc alloy layer 5 to be exposed at the both outer faces as shownin FIG. 3B with the nickel-zinc alloy layer 5 remaining without beingdissolved.

Then, a laser beam 12 was applied to a predetermined location to carryout drilling processing to bore a via hole 14 with a carbon dioxidelaser 13. For the irradiation conditions of the carbon dioxide laser 13,the frequency was 2000 Hz, the mask diameter was 5.0 mm, the pulse widthwas 60 μsec., the pulse energy was 16.0 mJ, the offset was 0.8 and thelaser beam diameter was 140 μm, so that a process diameter of 110 μm wasprovided. At this time, even if the nickel-zinc alloy layer 5 existed,drilling processability was not compromised at all, but rather asatisfactory via hole shape could be provided. Thereafter, desmeartreatment was carried out to smooth the inner surface of the via hole 14and remove remainders such as resin remaining on the bottom of the viahole 14, thereby providing a situation shown in FIG. 3C.

In addition, as an effect obtained in a overlapping way, it could beensured that due to a solution for desmear treatment, the resin of theinsulation layer 10 is prevented from being dissolved, andirregularities on the outer face of the plate are not vanished, becauseof existence of the nickel-zinc alloy layer 5 on the outermost layer.This is effective in the sense that adhesion to the substrate of theplated layer formed in the subsequent step is improved.

Here, the panel plating method was used to form a copper plated layer 15with average thickness of 15 μm on the entire surface of the substrateincluding the inner surface of the via hole 14. For copper platedconditions at this time, a copper sulfate solution was used withconcentrations of sulfuric acid and copper being 150 g/l and 65 g/l,respectively, and with liquid temperature of 45° C., current density of15 A/dm²and electrolysis time of 140 seconds. Then, an etching resistlayer 16 was formed on the surface of the copper plated layer 15 withthe use of a dry film as shown in FIG. 4E, and a circuit pattern wasdeveloped through light exposure on the etching resist layer 16 as shownin FIG. 5F, and an acid etchant for copper was used to carry out circuitetching, and the etching resist layer 16 was peeled to obtain aprinted-wiring board 18 with an outer circuit 17 as shown in FIG. 5G.

The printed-wiring board 18 obtained as described above was used tomeasure the peel strength at the interface between the outer circuit 17and the isolation layer 10. As a result, the dry peel strength was 1.89kgf/cm, and the level of UL heat resistance at rating 130° C. defined inthe UL 796 Standard was 0.85 kgf/cm, both well surpassing the values (10days) specifying the UL standard.

EXAMPLE 2

In this Example, the steps of producing a printed-wiring board with theuse of a copper foil for printed-wiring board comprising an alloy layerof nickel and zinc on the matte side of an electrodeposited copper foilwill be described. First, production of the copper foil forprinted-wiring board 1 will be described with reference to the drawings.Here, an electrodeposited copper foil having a cross section shownschematically in FIG. 1 for use in producing a copper foil havingnominal thickness of 18 μm, which had not been subjected to surfacetreatment (hereinafter referred to as “untreated copper foil”) was used.Then, a so called surface treatment apparatus was used to subject thisuntreated copper foil 2 to nodular treatment and surface treatment forforming the nickel-zinc layer.

In the surface treatment apparatus, copper microparticles 4 are firstdeposited on the surface of the matte side 3 of the untreated copperfoil 2 under burnt copper plating conditions, and seal plating wascarried out as level copper plating conditions so as to prevent thecopper microparticles 4 from being dropped off, thereby depositingstably the copper microparticles 4 on the matte side 3 of the untreatedcopper foil 2. For the burnt copper plating conditions for the coppermicroparticles 4, plating was carried out under conditions of currentdensity of 30 A/dm² and electrolysis time of 4 seconds by using aninsoluble anode (DSE) for the counter electrode to make the copper foilitself undergo cathode polarization, in a copper sulfate solution at aliquid temperature of 30° C. with concentrations of copper and sulfuricacid being 12 g/l and 180 g/l, respectively. For the level copperplating conditions for the copper microparticles 4, plating was carriedout under conditions of current density of 15 A/dm² and electrolysistime of 4 seconds with the use of a stainless plate for the counterelectrode to make the copper foil itself undergo cathode polarization,in a copper sulfate solution at a liquid temperature of 30° C. withconcentrations of copper and sulfuric acid being 40 g/l and 180 g/l,respectively.

Then, the nickel-zinc alloy layer 5 was formed on the surface with thecopper microparticles 4 provided thereon. For this nickel-zinc alloylayer 5, a pyrophosphate based solution was prepared using zincpyrophosphate (ZnP₂O₇·3H₂O), nickel sulfate (NiSO₄·7H₂O) and potassiumpyrophosphate (K₂P₄O₇) so that the solution had a composition with 0.2g/l of zinc, 2.3 g/l of nickel and 100 g/l of potassium pyrophosphate,and in the solution at a liquid temperature of 30° C., the copper foilitself was made to undergo cathode polarization using a stainless platefor the counter electrode under conditions of current density of 2 A/dm²and electrolysis time of 150 seconds, thereby providing an alloycomposition with 0.76 g/m² (76.0 wt %) of nickel and 0.24 g/cm² (24.0 wt%) of zinc. The weight thickness of the nickel-zinc alloy layer at thistime was 1.00 g/m². In concurrence with this formation of thenickel-zinc alloy layer 5 on the matte side 3, 0.10 g/m² of nickel-zinclayer was formed on the shiny side 6 of the untreated copper foil 2 as acorrosion prevention layer. In addition, the surface with thenickel-zinc alloy layer 5 formed thereon was treated with a silanecoupling agent and then dried to produce the copper foil forprinted-wiring board 1 shown in FIG. 1. However, the nickel-zinc alloylayer 5 formed on the surface of the shiny side 6, and the silanecoupling agent treated layer are not shown in the drawings.

Thereafter, the printed-wiring board 18 was produced through a methodsimilar to that used in Example 1, comprised of the steps shown in FIGS.2 to 5. This printed-wiring board 18 was used to measure the peelstrength at the interface between the outer circuit 17 and the isolationlayer 10. As a result, the dry peel strength was 1.89 kgf/cm, and thelevel of UL heat resistance at rating 130° C. defined in the UL 796Standard was 1.15 kgf/cm, both well surpassing the values (10 days)specifying the UL standard.

EXAMPLE 3

In this Example, the steps of producing a printed-wiring board using acopper foil for printed-wiring board comprising two layers, namelynickel and zinc layers on the nodular treatment side of anelectrodeposited copper foil will be described. First, production of thecopper foil for printed-wiring board 1 will be described with referenceto the drawings. Here, an electrodeposited copper foil having a crosssection shown schematically in FIG. 8 for use in producing a copper foilhaving nominal thickness of 18 μm, which had not been subjected tosurface treatment (hereinafter referred to as “untreated copper foil”)was used. Then, a so called surface treatment apparatus was used tosubject this untreated copper foil 2 to nodular treatment and surfacetreatment for forming the nickel and zinc layers.

In the surface treatment apparatus, copper microparticles 4 are firstdeposited on the surface of the matte side 3 of the untreated copperfoil 2 under burnt copper plating conditions, and seal plating wascarried out as level copper plating conditions so as to prevent thecopper microparticles 4 from being dropped off, thereby depositingstably the copper microparticles 4 on the matte side 3 of the untreatedcopper foil 2. For the burnt copper plating conditions for the coppermicroparticles 4, plating was carried out under conditions of currentdensity of 30 A/dm² and electrolysis time of 4 seconds by using aninsoluble anode (DSE) for the counter electrode to make the copper foilitself undergo cathode polarization, in a copper sulfate solution at aliquid temperature of 30° C. with concentrations of copper and sulfuricacid being 12 g/l and 180 g/l, respectively. For the level copperplating conditions for the copper microparticles 4, plating was carriedout under conditions of current density of 15 A/dm² and electrolysistime of 4 seconds by using the insoluble anode (DSE) for the counterelectrode to make the copper foil itself undergo cathode polarization,in a copper sulfate solution at a liquid temperature of 30° C. withconcentrations of copper and sulfuric acid being 40 g/l and 180 g/l,respectively.

Then, a nickel layer 5 was formed on the surface with coppermicroparticles 4 provided thereon. For this nickel layer 5, a nickelsulfate based solution was prepared so that the solution had acomposition with 300 g/l of nickel sulfate (NiSO₄·7H₂O), 50 g/l ofnickel chloride (NiCl₂) and 40 g/l of boric acid (H₃BO₃), and in thesolution at a liquid temperature of 30° C., the copper foil itself wasmade to undergo cathode polaraization with the use of a stainless platefor the counter electrode under conditions of current density of 24A/dm² and electrolysis time of 12.6 seconds, thereby electro-depositing8.24 g/m² of nickel.

Subsequently, a zinc layer 19 was formed on the surface of the nickellayer 5. With a solution having concentrations of zinc and potassiumpyrophosphate being 6 g/l and 100 g/l, respectively, the copper foilitself was made to undergo cathode polarization with the use of astainless plate for the counter electrode in the solution at a liquidtemperature of 25° C. under conditions of current density of 6 A/dm² andelectrolysis time of 2 seconds, thereby electrodepositing 0.20 g/m² ofzinc.

The reduced thickness of the nickel layer 5 and the zinc layer 19 is0.96 μm (0.96 +zinc) from Equation 1. In concurrence with this formationof this zinc layer 19, 0.02 g/m² of zinc layer was formed on the shinyside 6 of the untreated copper foil 2 as a corrosion prevention layer.In addition, the surface with the zinc layer 5 formed thereon wastreated with a silane coupling agent and then dried to produce thecopper foil for printed-wiring board 1 shown in FIG. 8. However, thezinc layer formed on the surface of the shiny side 6, and the silanecoupling agent treated layer are not shown in the drawings.

Thereafter, the printed-wiring board 18 was produced by a method similarto that used in Example 1, comprised of the steps shown in FIGS. 2 to 5.This printed-wiring board 18 was used to measure the peel strength atthe interface between the outer circuit 17 and the isolation layer 10.As a result, the dry peel strength was 1.89 kgf/cm, and the level of ULheat resistance at rating 130° C. defined in the UL 796 Standard was1.15 kgf/cm, both well surpassing the values (10 days) specifying the ULstandard.

EXAMPLE 4

Here, the case where the additive method was adopted for forming theouter circuit 17 will be described. Thus, the steps shown in FIGS. 2A to3C are similar to those of Example 1. Therefore, in order to preventredundancy, such steps will not be described here. Also, for the symbolsin the drawings, common symbols will be used wherever possible. Thesubsequent steps proceeds in accordance with the following flow. Theetching resist layer 16 was formed as shown in FIG. 6D on the surface ofthe exposed nickel-zinc alloy layer 5 of a substrate subjected to laserdrilling processing shown in FIG. 3C to provide a via hole shapetherein, and made to undergo desmear treatment, and a circuit patternwas developed by light exposure on the etching resist layer 16, and anetchant was used to etch the nickel-zinc alloy layer 5 in a circuitshape as shown in FIG. 7F, and the remaining etching resist layer 16 waspeeled off, thereby leaving only the nickel-zinc alloy layer 5 on thesite forming the outer circuit 17.

Then, a copper plated layer having average thickness of 15 μm was formedon the nickel-zinc alloy layer 5 shaped into a circuit and on the innerwall of the via hole, thereby obtaining a printed-wiring board as shownin FIG. 7G. The copper plating was carried out by first catalyzingpalladium and forming a copper layer with thickness of 1 μm to 2 μm byelectroless copper plating, followed by carrying out electrolysis copperplating under conditions of current density of 15 A/dm² with a coppersulfate solution at a liquid temperature of 45° C. having concentrationsof sulfuric acid of 150 g/l and copper of 65 g/l.

The printed-wiring board 18 obtained as described above was used tomeasure the peel strength at the interface between the outer circuit 17and the isolation layer 10. As a result, the dry peel strength was 1.76kgf/cm, and the level of UL heat resistance at rating 130° C. defined inthe UL 796 Standard was 1.03 kgf/cm, both well surpassing the values (10days) specifying the UL standard.

COMPARATIVE EXAMPLE 1

In this Comparative Example 1, the copper foil for printed-wiring board1 was produced in a method similar to that of Example 1 for producingthe printed-wiring board 18 in a similar way.

However, the composition of nickel and zinc in the nickel-zinc alloylayer 5 was purposely deviated from the range according to the presentinvention in which the content of nickel is 70 to 88 wt % and thecontent of zinc is the balance. Thus, for this nickel-zinc alloy layer5, a pyrophosphate based solution was prepared using zinc pyrophosphate(ZnP₂O₇·3H₂O), nickel sulfate (NiSO₄·7H₂O) and potassium pyrophosphate(K₂P₄O₇) so that the solution had a composition with 1.0 g/l of zinc,1.5 g/l of nickel and 100 g/l of potassium pyrophosphate, and in thesolution at a liquid temperature of 30° C., the copper foil itself wasmade to undergo cathode polaraization with the use of a stainless platefor the counter electrode under conditions of current density of 1 A/dm²and electrolysis time of 300 seconds, thereby providing an alloycomposition with 1.14 g/m² (59.1 wt %) of nickel and 0.79 g/cm² (40.9 wt%) of zinc. The weight thickness of the nickel-zinc alloy layer 5 was1.93 g/m². In concurrence with this formation of the nickel-zinc alloylayer 5 on the nodular treatment side 4, 0.10 g/m² of nickel-zinc layerwas formed on the shiny side 6 of the untreated copper foil 2 as acorrosion prevention layer.

Then, in the process of production of the printed-wiring board 18, theuntreated copper foil 2 on the both outer faces and the cupper componentof the copper microparticles 4 were first etched away for carrying outlaser drilling processing for the four-layer plate 11 shown in FIG. 2A,but when they were etched away, the nickel-zinc alloy layer 5 having theabove described composition was dissolved because the content of nickelin the nickel-zinc alloy layer 5 was low even if A process solution(manufactured by Meltex Co., Ltd.) being so called an alkali etchant wasused as a etchant for copper, thus making it impossible to conductselective etching. As a result, the nickel-zinc alloy layer 5 located onthe both outer faces in FIG. 3B was removed, and therefore theprinted-wiring board 18 could not be produced by a method similar tothat of Example 1.

COMPARATIVE EXAMPLE 2

In this Comparative Example 2, the copper foil for printed-wiring board1 was produced in a method similar to that of Example 1 to produce theprinted-wiring board 18 in a similar way.

However, the composition of nickel and zinc in the nickel-zinc alloylayer 5 was purposely deviated from the range according to the presentinvention in which the content of nickel is 70 to 88 wt % and thecontent of zinc is the balance. Thus, for this nickel-zinc alloy layer5, a pyrophosphate based solution was prepared using zinc pyrophosphate(ZnP₂O₇·3H₂O), nickel sulfate (NiSO₄·7H₂O) and potassium pyrophosphate(K₂P₄O₇) so that the solution had a composition with 0.6 g/l of zinc,10.0 g/l of nickel and 100 g/l of potassium pyrophosphate, and in thesolution at a liquid temperature of 30° C., the copper foil itself wasmade to undergo cathode polaraization with the use of a stainless platefor the counter electrode under conditions of current density of 0.8A/dm² and electrolysis time of 6000 seconds, thereby providing an alloycomposition with 7.74 g/m² (90.0 wt %) of nickel and 0.86 g/cm² (10.0 wt%) of zinc. The weight thickness of the nickel-zinc alloy layer 5 was8.60 g/m². In concurrence with this formation of the nickel-zinc alloylayer 5 on the nodular treatment side 4, 0.02 g/m² of nickel-zinc layerwas formed on the shiny side 6 of the untreated copper foil 2 as acorrosion prevention layer.

Then, in the process of production of the printed-wiring board 18, theuntreated copper foil 2 on the both outer faces and the cupper componentof the copper microparticles 4 were first etched away for carrying outlaser drilling processing for the four-layer plate 11 shown in FIG. 2A.When they were etched away. A process solution (manufactured by MeltexCo., Ltd.) being so called an alkali etching solution was used as anetchant for copper, whereby the nickel-zinc alloy layer 5 remainedwithout being dissolved, thus making it possible to leave thenickel-zinc alloy layer 5 exposed at the both outer faces as shown inFIG. 3B.

However, the content of zinc in the nickel-zinc alloy layer 5 was low,and therefore as a result of measuring the peel strength at theinterface between the outer circuit 17 and the isolation layer 10, thedry peel strength was 1.92 kgf/cm, and the level of UL heat resistanceat rating 130° C. defined in the UL 796 Standard was 0.50 kgf/cm,showing that the printed-wiring board 18 had poor UL heat resistance.

COMPARATIVE EXAMPLE 3

In this Comparative Example, the step of producing the printed-wiringboard using a copper foil for printed-wiring board comprising only anickel layer on the nodular treatment side of the electrodepositedcopper foil will be described. First, production of the copper foil forprinted-wiring board 1 will be described with reference to the drawings.Here, an electrodeposited copper foil having a cross section shownschematically in FIG. 8 for use in production of a copper foil havingnominal thickness of 18 μm, which had not been subjected to surfacetreatment (hereinafter referred to as “untreated copper foil”) was used.Then, a so called surface treatment apparatus was used to subject thisuntreated copper foil 2 to nodular treatment and surface treatment forforming the nickel layer.

In the surface treatment apparatus, copper microparticles 4 are firstdeposited on the surface of the matte side 3 of the untreated copperfoil 2 under burnt copper plating conditions, and seal plating wascarried out as level copper plating conditions so as to prevent thecopper microparticles 4 from being dropped off, thereby depositingstably the copper microparticles 4 on the matte side 3 of the untreatedcopper foil 2. For the burnt copper plating conditions for the coppermicroparticles 4, plating was carried out under conditions of currentdensity of 30 A/dm² and electrolysis time of 4 seconds by using aninsoluble anode (DSE) for the counter electrode to make the copper foilitself undergo cathode polarization, in a copper sulfate solution at aliquid temperature of 30° C. with concentrations of copper and sulfuricacid being 12 g/l and 180 g/l, respectively. For the level copperplating conditions for the copper microparticles 4, plating was carriedout under conditions of current density of 15 A/dm² and electrolysistime of 4 seconds by using the insoluble anode (DSE) for the counterelectrode to make the copper foil itself undergo cathode polarization,in a copper sulfate solution at a liquid temperature of 30° C. withconcentrations of copper and sulfuric acid being 40 g/l and 180 g/l,respectively.

Then, a nickel layer 5 was formed on the surface with coppermicroparticles 4 provided thereon. For this nickel layer 5, a nickelsulfate based solution was prepared so that the solution had acomposition with 300 g/l of nickel sulfate (NiSO₄·7H₂O), 50 g/l ofnickel chloride (NiCl₂) and 40 g/l of boric acid (H₃BO₃), and in thesolution at a liquid temperature of 30° C., the copper foil itself wasmade to undergo cathode polaraization with the use of a stainless platefor the counter electrode under conditions of current density of 24A/dm² and electrolysis time of 12.6 seconds, thereby electro-depositing8.15 g/m² of nickel.

The reduced thickness of the nickel layer 5 is 0.92 μm. In addition, thesurface with the nickel layer 5 formed thereon was treated with a silanecoupling agent and then dried to produce the copper foil forprinted-wiring board 1 shown in FIG. 8. However, the silane couplingagent treated layer is not shown in the drawings.

Thereafter, the printed-wiring board 18 was produced by a method similarto that used in Example 1, comprised of the steps shown in FIGS. 2 to 5.This printed-wiring board 18 was used to measure the peel strength atthe interface between the outer circuit 17 and the isolation layer 10.As a result, the dry peel strength was 1.85 kgf/cm, and the level of ULheat resistance at rating 130° C. defined in the UL 796 Standard was0.30 kgf/cm, apparently showing that the printed-wiring board 18 hadpoor UL heat resistance.

INDUSTRIAL APPLICABILITY

By using the copper foil for printed-wiring board according to thepresent invention, laser drilling processing can easily be carried outin the process of a printed-wiring board, and selective etchingadvantageous for formation of a fine pitch circuit can be conducted, andhigh UL heat resistance can be ensured for a conductor circuit finallyformed in the printed-wiring board. This copper foil for printed-wiringboard excellent in total balance, which is the first of its type, willmake it possible to introduce high quality printed-wiring boards to themarket.

1. A copper foil for a printed-wiring board, said copper foil comprisinga nodular treated side to be bonded to a substrate, wherein a nickellayer is provided on the nodular treated side, wherein the thickness (X)of the nickel layer is 0.7 g/m² to 45 g/m²; a zinc layer or a zinc alloylayer wherein the thickness (Y) of the zinc layer is 0.01 g/m² to 2 g/m²is provided on the nickel layer and an equivalent thickness (T) ofnickel layer and zinc layer or zinc alloy layer calculated from Equation1 is smaller than or equal to 5 μm,T=(X/8.85)+(Y/7.12)(μm)  Equation 1 Specific gravity of nickel: 8.85g/cm³ Specific gravity of zinc: 7.12 g/cm³.
 2. A copper clad laminatecomprising the copper foil of claim
 1. 3. The copper foil for aprinted-wiring board according to claim 1, wherein the thickness (X) ofthe nickel layer is 0.7 g/m² to 45 g/m², and the thickness (Y) of thezinc layer containing n kinds of alloying elements is 0.01 g/m² to 2g/m², and the equivalent thickness (T) of the nickel layer and zinclayer is determined by the calculation procedure shown in Equation 2 issmaller than or equal to 5 μm, Equation 2 ρ_(sum) represents specificgravity of the zinc alloy. This is a value converted asρ_(sum)={7.12×a+ρ_(Men)×b_(n))]/100, provided that the zinc alloy iscomprised of a % by weight of Zn and n kinds of alloying elements, eachalloying element is represented by _(Men), the content of the alloyingelement is ρ_(Men).
 4. A copper clad laminate comprising the copper foilof claim 3.